The invention relates to a terminal-processed structure of a tape-shaped cable including a plurality of coaxial cables arranged in parallel and a method for processing a terminal of the same, and more particularly to a method for processing a terminal of a fine tape-shaped cable used as a wiring material around a liquid crystal display for a personal computer or a display for an ultrasonic diagnostic apparatus requiring high resolution, and to a terminal-processed structure of the tape-shaped cable.
As a wiring material in LCD (liquid crystal display) used for a note-book type personal computer or the like, an FPC (flexible print circuit board) has been used commonly heretofore. Recently, higher speed of image signal processing is required for improving the image quality of LCD. To increase signal processing speed, fine coaxial cables have been applied to wiring around displays in place of FPC.
Tape-shaped cables composed of fine coaxial cables are used more and more as demands for more compact, thinner and lighter personal computers, such as note-book type and portable personal computers, are growing rapidly.
However, for connecting a number of fine coaxial cables with an FPC, a PCB (print circuit board) or a connector terminal, terminal processing of the cable is required so as to ground all of the outer conductors without failure and to keep the inner conductors of respective cores to be positioned in a predetermined pitch. It has been much troublesome to carry out such terminal processing of fine coaxial cables.
In an attempt to solve the problem, a conventional method for processing a terminal of a tape-shaped cable is disclosed in Japanese Patent Application Laid-open No. Hei 10-144145, in which sheaths of the coaxial cables in portions close to the terminal are removed so as to expose outer conductors of the coaxial cables, two grounding metal bars are soldered on the outer conductors thus exposed at respective positions, and one of the metal bars and the outer conductors positioned on the tip side relative to the other metal bar are removed together.
In the conventional method for processing the terminal of the tape-shaped cable, however, there are disadvantages in that the use of two metal bars is laborious and increases the cost for terminal processing because one of the metal bars is discarded together with the removed portions of the outer conductors, and the mechanical and electrical characteristics are not obtained stably in the soldering of the metal bars to the respective outer conductors.
Accordingly, it is an object of the invention to provide a terminal-processed structure of a tape-shaped cable including coaxial cables having very small diameters arranged in parallel and a method for processing a terminal of the same which ensure, with less cost and labor, grounding of the outer conductors of the cables without failure and the positions of inner conductors at the terminal.
It is another object of the invention to provide a terminal-processed structure of a tape-shaped cable and a method for processing a terminal of the same in which grounding plates are connected in mechanical and electrical stability to outer conductors.
According to the first feature of the invention, a terminal-processed structure of a tape-shaped cable including a plurality of coaxial cables arranged in parallel, comprises:
inner conductors arranged in parallel with a predetermined pitch;
insulative layers for insulating the inner conductors except for a predetermined portion thereof, thereby providing exposed inner conductors each having a predetermined length;
outer conductors provided on the insulative layers except for a predetermined portion thereof, thereby providing exposed insulative layers on both sides of the exposed inner conductors;
a solder layer for covering the outer conductors, the solder layer having opposite flat surfaces;
grounding plates soldered to the opposite flat surfaces of the solder layer;
sheaths provided on outer peripheries of the outer conductors at positions where the solder layer does not cover the outer conductors; and
insulative tapes for arranging the plurality of coaxial cables in parallel with the predetermined pitch, the insulative tapes adhering to the sheaths, and each coaxial cable including one of the inner conductors, one of the insulative layers, one of the outer conductors, and one of the sheaths.
According to the second feature of the invention, a method for processing a terminal of a cable having a plurality of coaxial cables arranged in parallel, comprises the steps of:
removing sheaths of the coaxial cables in a portion close to the terminal so as to expose outer conductors of the coaxial cables;
covering the entirety of outer conductors thus exposed with a solder layer;
separating the solder layer and the outer conductors into two portions at a predetermined longitudinal position of the solder layer; and
removing the portion of the solder layer and the outer conductors positioned on the tip side relative to the predetermined longitudinal position, in a lump, so as to expose insulative layers of the coaxial cables.
In a preferred embodiment, the solder layer and the outer conductors are separated at the predetermined longitudinal position by bending the tape-shaped cable up and down in the vertical direction (perpendicular to the longitudinal direction). Alternatively, a groove may be formed in the direction perpendicular to the longitudinal direction of the cable at the predetermined position of the solder layer so that the solder layer and the outer conductors may be cut by pulling or bending them with the fulcrum at the groove thus formed, whereby the solder layer and the outer conductors are separated at the predetermined position. The separation of the outer conductors by the help of groove formed on the solder layer is preferable, taking account of the evenness of the cutting surface.
The groove may be formed by scraping a surface portion of the solder layer by means of a mechanical knife. Alternatively, the groove may be formed by laser processing whereby the solder layer is melted and removed at a position where the laser light is irradiated. The separation of the outer conductors at the grooved position by pulling or bending is performed more easily after laser processing because the solder is also removed between the cables by laser processing to form notches (perforations) in a broken line like a machine-sawing line along the processing groove.
Further, it is preferred that a conductive plate is soldered to be fixed on the flat surface of the solder layer which is left after removal of the separated solder layer and outer conductors, while the pitch of insulative cores is kept by the solder layer. Thus, linearity in the cross-section of the outer conductors is ensured at the processed terminal even if the surface of the separated outer conductors and solder layer is uneven, facilitating the alignment when the terminal-processed tape-shaped cable is applied to a connector.
It is preferred that the exposed portions of insulative layers of the coaxial cables are fixed at a predetermined pitch before they are removed to expose inner conductors of the coaxial cables.
Before use of the terminal-processed tape-shaped cable according to the invention, exposed portions of the insulative layers are removed so that inner conductors of the coaxial cables are exposed.